Hi, I am trying to make a script that will upload files and show a progress bar and I've come so far that I can upload the file but the progress bar that appear for each file will not grow with green goo, you know?

you are trying to access a <progress> element with id="progressBar", but with this code

pbar.setAttribute('id', 'progressBar' + i);

you created the <progress> elements with id="progressBar0", "progressBar1" etc. respectively. So there is no <progress> element with id="progressBar". The same can be applied to the <div> with id="report"